This invention relates to printers and more particularly to an improved arrangement for automatically resetting the print head to its prior predetermined gap spacing with respect to said print surface following movement of the print head away from the print surface for servicing.
Serial printers such as matrix printers are well known in the prior art. A fairly common type of such printer involves a plurality of print wires or styli which are arranged in a vertical line. These styli are maintained in a spaced apart arrangement in a print head. The head is supported on a carriage which in turn is caused to traverse a line of movement across a record medium. As the carriage shifts the print head through successive columns along a line of movement on the record medium, a dot pattern of alphanumeric characters is produced on the record medium by selective displacement or extension of individual print styli in their successive column positions for impacting the record medium through the inked ribbon.
Whenever ribbon has to be changed or new paper fed into the machine, the print head must be retracted for ease of operation. Upon servicing the head must be returned to its printing position. It is important that the head be returned to a predetermined gap spacing with respect to the print surface of the record medium in order to insure uniformity of printing. Where the print head involves a stylus printer, it is known that the force of the impacting styli against the ribbon varies with the gap spacing. In a worst case condition, the wires never reach the ribbon to achieve printing. If the spacing is too close, smudging and tearing of the inked ribbon will occur. Between these two extremes the density or darkness of printing will vary. Accordingly, it is important that the print head be returned to its previous acceptable printing spacing with respect to the record medium in order to maintain uniformity of printing. Systems heretofore proposed have necessitated a manual adjustment of the gap setting between the print head and the record medium after every servicing of the print head. This oftentimes requires trial and error changes to achieve the desired print quality and results in undesirable delays in printing. In addition, other systems have employed arrangements where printing has to be suspended while the print head gap spacing is adjusted. These problems of spacing become more acute as the print speed increases, since the rebound time of the print styli and the gap spacing become increasingly critical in achieving uniformity of printing.